Dielectric properties and structural dynamics of melt compounded hot-pressed poly(ethylene oxide)–organophilic montmorillonite clay nanocomposite films

The dielectric properties of melt compounded hot-pressed nanocomposite films consisting of a poly(ethylene oxide) (PEO) and organophilic montmorillonite (OMMT) clay surface modified with trimethyl stearyl ammonium as filler with increasing amount up to 20 wt.% OMMT were investigated in a frequency range of 20 Hz–1 MHz at 30 °C. The predominance of OMMT exfoliated structures in PEO–OMMT nanocomposites were recognized by a decrease of the real part of complex dielectric function. OMMT concentration dependent dielectric and electric modulus relaxation times have revealed that the interactions compatibility between PEO molecules and dispersed OMMT nano-platelets in PEO matrix governs the PEO segmental dynamics. A.C. conductivity of these nanocomposites increases by two orders of magnitude in the experimental frequency range.     

Graphite oxide/poly(methyl methacrylate) nanocomposites prepared by a novel method utilizing macroazoinitiator

Graphite oxide (GO)/poly(methyl methacrylate) (PMMA) nanocomposites were prepared by a novel method utilizing macroazoinitiator (MAI). The MAI, which has a poly(ethylene oxide) (PEO) segment, was intercalated between the lamellae of GO to induce the inter-gallery polymerization of methyl methacrylate (MMA) and exfoliate the GO. The morphological, conductivity, thermal, mechanical and rheological properties of these nanocomposites were examined and compared with those of intercalated nanocomposites prepared by polymerization with the normal radical initiator, 2,2′-azobisisobutyronitrile. The improvement in conductivity by GO was more evident in exfoliated nanocomposites compared to that of intercalated nanocomposites. For example, a conductivity of 1.78 × 10⁻⁷ S/cm was attained in the exfoliated nanocomposite prepared with 2.5 parts GO per 100 parts MMA, which was about 50-fold higher than that of the intercalated nanocomposite. The thermal, mechanical and rheological properties also indicate that thin GO with a high aspect ratio is finely dispersed and effectively reinforced the PMMA matrix in both exfoliated and intercalated nanocomposites.     

Morphology and mechanical properties of bisphenol A polycarbonate/poly (styrene-co-acrylonitrile) blends based clay nanocomposites

Two organic modified clays (Cloisite®30B (CL30B) and PCL/Cloisite®30B masterbatch (MB30B)) were used to improve the mechanical properties of polycarbonate (PC)/poly (styrene-co-acrylonitrile) (SAN) blends. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements of the melt blended nanocomposites revealed that partially exfoliated and partially degraded structure was obtained and the clay platelets were located mostly in the SAN phase and at the two-phase boundary. Dispersion of the clay platelets is better when MB30B were used. The mechanical properties of the clays filled nanocomposites vary accordingly and when MB30B is used better mechanical properties can be achieved. Tensile strength increases 41% at maximum as the CL30B loading is 5 wt.%, while elongation at break decreases dramatically. Impact strength can be improved up to 430% compared to the pure blend when 1 wt.% MB30B was used.     

Morphology,thermal and mechanical properties of PVC/MMT nanocomposites prepared by solution blending and solution blending + melt compounding

Two types of montmorillonite (MMT), natural sodium montmorillonite (Na-MMT) and organically modified montmorillonite (OMMT), in different amounts of 1, 2, 5, 10 and 25 phr (parts per hundred resin), were dispersed in rigid poly (vinyl chloride) by two different methods: solution blending and solution blending + melt compounding. The effects on morphology, thermal and mechanical properties of the PVC/MMT nanocomposites were studied by varying the amount of Na-MMT and OMMT in both methods. SEM and XRD analysis revealed that possible intercalated and exfoliated structures were obtained in all of the PVC/MMT nanocomposites. Thermogravimetric analysis revealed that PVC/Na-MMT nanocomposites have better thermal stability than PVC/OMMT nanocomposites and PVC. In general, PVC/MMT nanocomposites prepared by solution blending + melt compounding revealed improved thermal properties compared to PVC/MMT nanocomposites prepared by solution blending. Vicat tests revealed a significant decrease in Vicat softening temperature of PVC/MMT nanocomposites prepared by solution blending + melt compounding compared to unfilled PVC.     

Improving the mechanical properties of thermoplastic starch/poly(vinyl alcohol)/clay nanocomposites

Thermoplastic starch/poly(vinyl alcohol) (PVOH)/clay nanocomposites, exhibiting the intercalated and exfoliated structures, were prepared via melt extrusion method. The effects of clay cation, water, PVOH and clay contents on clay intercalation and mechanical properties of nanocomposites were investigated. The experiments were carried out according to the Taguchi experimental design method. Montmorillonite (MMT) with three types of cation or modifier (Na⁺, alkyl ammonium ion, and citric acid) was examined. The prepared nanocomposites with modified montmorillonite indicated a mechanical improvement in the properties in comparison with pristine MMT. It was also observed that increases in tensile strength and modulus would be attained for nanocomposite samples with 10%, 5% and 4% (by weight) of water, PVOH and clay loading, respectively. The clay intercalation was examined by X-ray diffraction (XRD) patterns. The chemical structure and morphology of the optimum sample was also probed by FTIR spectroscopy and transmission electron microscopy (TEM).     

Elastomeric epoxy nanocomposites: Nanostructure and properties

In polymer layered silicate nanocomposites, significant differences have been reported between the effects of the nano-reinforcement on rigid and elastomeric nanocomposites. In this paper, we have studied elastomeric nanocomposites based upon DGEBA epoxy resin filled with montmorillonite (MMT) and cured with a long-chain polyoxypropylene diamine, for comparison with analogous rigid nanocomposites. Ultrasonic mixing was used to disperse the MMT in the matrix to improve homogeneity and decrease the agglomerate size. Two different methods of nanocomposite preparation were used in which the MMT was first swollen with either the curing agent or the epoxy before the addition of, respectively, DGEBA or diamine. A better dispersion of the nanoclay in the matrix and a greater amount of intercalation occurred when the MMT was first swollen with the diamine. The effect of MMT concentrations up to 8 wt.% on the mechanical behaviour of the epoxy/MMT nanocomposites was investigated. It was found that the addition of MMT increased the tensile strength and modulus, although SAXS and TEM indicated that a significant fraction of the clay layers were not exfoliated. Nevertheless, the addition of the clay resulted in changes in the fracture surfaces, as indicated by SEM, consistent with the tensile results and indicative of toughening.     

Synthesis and characterization of biodegradable poly(l-lactide)/layered double hydroxide nanocomposites

This study reports the preparation and physical properties of biodegradable nanocomposites fabricated using poly(l-lactide) (PLLA) and magnesium/aluminum layered double hydroxide (MgAl-LDH). The MgAl-LDH with molar ratio of Mg/Al = 2 were synthesized by the co-precipitation method. In order to improve the chemical compatibility between PLLA and LDH, the surface of LDH was organically-modified by polylactide with carboxyl end group (PLA–COOH) using ion-exchange process. Then, the PLLA/LDH nanocomposites were prepared by solution intercalation of PLLA into the galleries of PLA–COOH modified LDH (P-LDH) in tetrahydrofuran solution. Both X-ray diffraction data and Transmission electron microscopy images of PLLA/P-LDH nanocomposites indicate that the P-LDHs are randomly dispersed and exfoliated into the PLLA matrix. Mechanical properties of the fabricated 1.2 wt.% PLLA/P-LDH nanocomposites show significant enhancements in the storage modulus when compared to that of neat PLLA. Adding more P-LDH into PLLA matrix induced a decrease in the storage modulus of PLLA/P-LDH nanocomposites, probably due to the excessive content of PLA–COOH moleculars with low mechanical properties. The thermal stability and degradation activation energies of the PLLA and PLLA/P-LDH nanocomposites can also be discussed.     

Dielectric characteristics of poly(N-vinylcarbazole) and its nanocomposites with ZnO and acetylene black

Dielectric constant and dielectric loss parameters of poly(N-vinylcarbazole) homopolymer and several nanocomposites of poly(N-vinylcarbazole) with ZnO were studied as a function of frequency. In the low frequency range (0–20 kHz) the dielectric constant values of the base polymer varied from ∼30 to ∼2, and the same for the composite varied from 8500 to 2000 (4.54), 5000 to 1000 (2.63) and 2000 to 500 (1.17), the figures in parenthesis denoting the ratio of ZnO:PNVC in the nanocomposites. Likewise, dielectric loss parameters were found to be (7–10 × 10⁻³) for the homopolymer and 4.0, 2.5 and 1.25 for the three PNVC–ZnO composites respectively. Notably, a mechanical mixture of ZnO and PNVC (1.17) exhibited much lower dielectric constant (400–25) and loss parameters (0.14–0.065). These features imply polarization was differently affected depending on factors such as grain size and grain-boundary interfaces being formed in these systems. Tan δ–temperature variation for the composites revealed the occurrence of a maximum between 60 and 70 °C. These features signified dipole group loss in the composite. Dielectric constant of a conducting nanocomposite of poly(N-vinylcarbazole) with acetylene black revealed very low negative value tending to zero at high frequency.     

Effects of modified Clay on the morphology and thermal stability of PMMA/clay nanocomposites

The potential to improve the mechanical, thermal, and optical properties of poly(methyl methacrylate) (PMMA)/clay nanocomposites prepared with clay containing an organic modifier was investigated. Pristine sodium montmorillonite clay was modified using cocoamphodipropionate, which absorbs UVB in the 280–320 nm range, via ion exchange to enhance the compatibility between the clay platelets and the methyl methacrylate polymer matrix. PMMA/clay nanocomposites were synthesized via in situ free-radical polymerization. Three types of clay with various cation-exchange capacities (CEC) were used as inorganic layered materials in these organic–inorganic hybrid nanocomposites: CL42, CL120, and CL88 with CEC values of 116, 168, and 200 meq/100 g of clay, respectively. We characterized the effects of the organoclay dispersion on UV resistance, effectiveness as an O₂ gas barrier, thermal stability, and mechanical properties of PMMA/clay nanocomposites. Gas permeability analysis demonstrated the excellent gas barrier properties of the nanocomposites, consistent with the intercalated or exfoliated morphologies observed. The optical properties were assessed using UV–Visible spectroscopy, which revealed that these materials have good optical clarity, UV resistance, and scratch resistance. The effect of the dispersion capability of organoclay on the thermal properties of PMMA/clay nanocomposites was investigated by thermogravimetric analysis and differential scanning calorimetry; these analyses revealed excellent thermal stability of some of the modified clay nanocomposites.     

Compatibilizing effect of acrylic acid modified polypropylene on the morphology and permeability properties of polypropylene/organoclay nanocomposites

This work dealt with the morphology and permeability properties of polypropylene/organoclay nanocomposites prepared using an acrylic acid grafted polypropylene (PP-g-AA) as compatibilizing agent. Two PP-g-AA containing the same acrylic acid content (6 wt.%) and having different molar masses were tested. The o-MMT content was 0, 1 or 5 wt.% and the PP-g-AA/o–MMT mass ratio was 0/1, 1/1, 2/1 or 5/1. Results of wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) showed that without the PP-g-AA, the o-MMT was dispersed in the PP/o-MMT in a micrometer scale, similar to a conventional microcomposite. With the PP-g-AA, the o-MMT was much better dispersed and its interlayers were intercalated and partly exfoliated by the polymer chains. CO₂ permeability values decreased for all samples with the incorporation of the organoclay. The compatibilized samples showed a more significant reduction in CO₂ permeability, up to 50% when compared to the neat PP. In general, the PP-g-AA acted satisfactorily in compatibilizing PP/organoclay nanocomposites. Moreover, samples prepared with the compatibilizer/organoclay ratio of 5/1 had better barrier properties.     

Carbohydrate derived copoly(lactide) as the compatibilizer for bacterial cellulose reinforced polylactide nanocomposites

A novel, entirely bio-derived polylactide carbohydrate copolymer (RP1) is used as a compatibilizer, to produce bacterial cellulose (BC) poly(l-lactide) (PLLA) nanocomposites with improved mechanical properties. Contact angle measurements of RP1 droplets on single BC nanofibres proved that it has a higher affinity towards BC than PLLA. RP1 has a comparable Young’s modulus, but lower tensile strength, than PLLA. When RP1 was blended with PLLA at a concentration of 5 wt%, the tensile modulus and strength of the resulting polymer blend decreased from 4.08 GPa and 63.1, respectively, for PLLA to 3.75 GPa and 56.1 MPa. A composite of BC and PLLA (with 5 wt% RP1 and 5 wt% BC) has a higher Young’s modulus and tensile strength, compared to either pure PLLA or PLLA–BC nanocomposites.     

The preparation of high performance and conductive poly (vinyl alcohol)/graphene nanocomposite via reducing graphite oxide with sodium hydrosulfite

Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7 wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene.     

Morphology,rheology and mechanical properties of polypropylene/ethylene–octene copolymer/clay nanocomposites: Effects of the compatibilizer

The objective of this study was to investigate the effects of two compatibilizers, namely maleated polypropylene (PP-g-MA) and maleic anhydride grafted poly (ethylene-co-octene) (EOC-g-MA), on the morphology and thus properties of ternary nanocomposites of polypropylene (PP)/ethylene–octene copolymer (EOC)/clay nanocomposite. In this regard the nanocomposites and their neat polymer blend counterparts were processed twice using a twin screw extruder. X-ray diffraction, transmission electron microscopy, Energy dispersive X-ray spectroscopy, and scanning electron microscopy were utilized to characterize nanostructure and microstructure besides mechanical and rheological behaviors of the nanocomposites. Clay with intercalated structure was observed in EOC phase of the PP/EOC/clay nanocomposite. Better dispersion state of the intercalated clay in EOC phase was observed by adding EOC-g-MA as a compatibilizer. On the other hand, adding PP-g-MA resulted in migration of the intercalated clay from the EOC to the PP and to the interface regions. It was also demonstrated that the elastomer particles became smaller in size where clay was present. The finest and the most uniform morphology was found in the PP/EOC/clay nanocomposite. In addition, the rheological results illustrated a higher complex viscosity and storage modulus for PP/EOC/PP-g-MA/clay nanocomposite in which clay particles were present in the matrix. Mechanical assessments showed improvements in the toughness of the nanocomposites with respect to their neat blends, without significant change in stiffness and tensile strength values. These results highlight a toughening role of clay in the polymer blend nanocomposites studied.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

PHBV nanocomposites based on organomodified montmorillonite and halloysite: The effect of clay type on the morphology and thermal and mechanical properties

The aim of this study was to evaluate the effect of the addition of two types of nanoparticles, organomodified montmorillonite Cloisite® 30B (C-30B), and a tubular like clay, halloysite (HNT), on the morphology and thermal and mechanical properties of poly(hydroxybutyrate-co-hydroxyvalerate) – PHBV nanocomposites. TEM and WAXD results showed a combination of a few tactoids and a partially exfoliated structure for PHBV/C-30B nanocomposites and a good dispersion of HNT in the PHBV matrix. DSC analysis indicated a lower nucleation density with the addition of nanoparticles. Furthermore, the presence of C-30B led to the formation of double melting peaks, related to different crystalline phases. However, a higher melting temperature was obtained for PHBV/HNT nanocomposites. A general increase in the Young’s modulus was observed. However, for PHBV/C-30B nanocomposites, this enhancement was at the expense of the strain at break and impact strength, probably due to the degradation of the polymer during processing.     

Preparation of the acidic PVA/MMT nanocomposite polymer membrane for the direct methanol fuel cell (DMFC)

A novel nanocomposite polymer electrolyte membrane composed of PVA polymer matrix and nanosized Montmorillonite (MMT) filler, was prepared by a solution casting method. The characteristic properties of the PVA/MMT nanocomposite polymer membrane were investigated using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), atomic force microscopy (AFM), micro-Raman spectroscopy, and the AC impedance method. The PVA polymer directly blended with nanosized MMT filler (2-20 wt.%) showed good ionic conductivity, thermal, and mechanical properties. The highest ionic conductivity value for the acidic PVA/10 wt.%MMT nanocomposite polymer membrane was around 0.0368 S cm^− 1 at 30 °C. The methanol permeability (P) value was 3-4 × 10^− 6 cm² s^− 1. It was revealed that the addition of nanosized MMT fillers into the PVA matrix could markedly improve the electrochemical properties of the PVA/MMT nanocomposite membrane. In fact, the PVA/MMT nanocomposite polymer membrane appears to be a good candidate for the DMFC applications.     

Local thermal-mechanical analysis of ultrathin interfacially mixed poly(ethylene oxide)/poly(acrylic acid) layer-by-layer electrolyte assemblies

Ion conductivities of layer-by-layer (LBL) assemblies of solid thin film polyelectrolyte systems involving poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) were found to be a strong function of the number of bilayer stacks, n, with conductivities approaching 10^− 7 S/cm for n < 10, compared to 10^− 9 S/cm for n ≥ 10 and 10^− 10 S/cm for bulk PEO. Increased ion conductivity for low LBL stack numbers (n < 10) originated to part from an effective suppression of the PEO crystallization via PEO/PAA blending, which could be inferred from local glass transition temperature measurements involving shear modulation force microscopy. Another phenomenon responsible for high conductivity in thin films was found in the in-plane phase heterogeneity of PEO and PAA. Increased ion conductivity for larger LBL stacks (n ≥ 10) were attributed to low concentration autoblending caused by PEO-PAA hydrogen bonding, and an average layer thickness of noticeably less than 100 nm. The effect of interfacial constraints was evident in the degree of intermixing, addressed by a thin film extended Fox blend analysis, in the glass and melting transitions of PEO and PAA pure film components. While the glass transition value of PAA decreased by 55% to 46 °C for an 8 nm film, the melting transition for PEO decreased by 15% to 64 °C caused by surface tension effects.     

Exfoliated poly(methyl methacrylate)/MgFe-layered double hydroxide nanocomposites with small inorganic loading and enhanced properties

The novel exfoliated polymer nanocomposites (PMMA/MgFe(DS)-LDH) were synthesized by in situ polymerization based on poly(methyl methacrylate) (PMMA) and dodecyl sulfate-intercalated MgFe-layered double hydroxide (MgFe(DS)-LDH). The participation of Fe³⁺ ion is found to play an important role in the improvement of thermal stability of nanocomposites with small inorganic loading and well-dispersed inorganic components. The thermal degradation mechanism was discussed.     

Highly conducting poly(methyl methacrylate)/carbon nanotubes composites: Investigation on their thermal, dynamic-mechanical, electrical and dielectric properties

Nanocomposites of poly(methyl methacrylate) (PMMA) containing various multi-walled carbon nanotubes (MWCNT) contents were prepared using melt mixing. Several techniques were employed to study the influence of the MWCNT addition on the thermal, mechanical, electrical and dielectric properties of the PMMA matrix. The electrical percolation threshold (p_c) was found to be 0.5 vol.% by performing AC and DC conductivity measurements. Significantly high conductivity levels (σ_dc) were achieved: σ_dc exceeds 10⁻² S/cm already at 1.1 vol.%, the criterion for EMI shielding (σ_dc > 10⁻¹ S/cm) is fulfilled at 2.9 vol.%, and the highest loaded sample (5.2 vol.%) gave a maximum value of 0.5 S/cm. Dielectric relaxation spectroscopy measurements in broad frequency (10⁻¹−10⁶ Hz) and temperature ranges (−150 to 170 °C) indicated weak polymer-filler interactions, in consistency with differential scanning calorimetry and dynamic-mechanical analysis findings. Weak polymer-filler interactions and absence of crystallinity facilitate the achievement of high conductivity levels in the nanocomposites.     

Preparation of polymer/LDH nanocomposite by UV-initiated photopolymerization of acrylate through photoinitiator-modified LDH precursor

The exfoliated polymer/layered double hydroxide (LDH) nanocomposite by UV-initiated photopolymerization of acrylate systems through an Irgacure 2959-modified LDH precursor (LDH-2959) as a photoinitiator complex was prepared. The LDH-2959 was obtained by the esterification of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) with thioglycolic acid, following by the addition reaction with 3-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), finally intercalation into the sodium dodecyl sulfate-modified LDH. For comparison, the intercalated polymer/LDH nanocomposite was obtained with additive Irgacure 2959 addition. From the X-ray diffraction (XRD) measurements and HR-TEM observations, the LDH lost the ordered stacking-structure and well dispersed in the polymer matrix at 5 wt% LDH-2959 loading. The glass transition temperature of UV-cured exfoliated nanocomposites increased to 64 °C from 55 °C of pure polymer without LDH addition. The tensile strength was improved from 10.1 MPa to 25.2 MPa, as well the Persoz hardness enhanced greatly, while the elongation at break remained an acceptable level.